Whato - I've done a few disco type things in the past, and working on one right now.
Bass - Keep it simple, repeat it, work hard on the timing, play it all the way through (don't do a couple of bars and loop). see the current post about recording bass in the 'Recording' part of the forum.
Strings - Keep to 1 or 2 layers, max of 3 notes in the chord, I use MAGIX independence, that's really good, if you after that typical disco intro. (so cool), that's a job for a MIDI keys person, out of my league I'm afraid, wouldn't attempt it.
Hope this helps.
Rich